Singlet Oxygen (1ΔgO2) as the Principal Oxidant in Myeloperoxidase-Mediated Bacterial Killing in Neutrophil Phagosome

Abstract

Intraphagosomal viability of wild type E. coli and lycopene (a powerful 1O2 quencher)-producing transformant E. coli was investigated using human polymorphonuclear leukocytes as the cells for phagocytosis of opsonized viable bacteria. While the viability of both wild type and the transformant E. coli decreased very rapidly in the phagosome, but the viability of the lycopene-transformant in phagosomes was about 1.7 times higher than that of wild type E. coli after 5 min of incubation. The results were very similar to the results obtained when E. coli strains were exposed to 1O2 generated in myeloperoxidase-H2O2-Br− system (a pure 1O2 generating system) at pH 4.5. The reason for HOCl, which may be generated in the myeloperoxidase-H2O2-Cl− system under physiological conditions but does not become involved in bactericidal action, could be explained by the near neutral pH in phagosomes at which bacterial killing by chlorination is extensively attenuated. This is the first report which proved 1O2-mediated bacterial killing in neutrophil-bacterial phagosomal system.